This invention relates to a device and a method for controlling a motor which performs a speed feedback control such that the speed of a body driven by the motor is consistent with a target speed.
There is a wide variety of bodies driven by a motor. One of such driven bodies is a carriage mounting a recording head thereon in a serial printer is one of them. A known method for controlling a motor when driving a carriage includes a position feedback control as well as a speed feedback control so that not only the speed but also the stop position of the carriage can be controlled.
FIG. 25 shows a particular structure of a motor control device including both a position feedback control and a speed feedback control. As shown in FIG. 25, a conventional motor control device 100 includes a position feedback (FB) controller 101, and a speed feedback controller 105. The position feedback controller 101 compares a current position Xn of a controlled body (carriage) 107 with a predetermined target stop position Xt. In order to make the position Xn consistent with the position Xt, the position feedback controller 101 performs a position feedback control and outputs a speed directive v corresponding to a difference between the positions Xn and Xt. The speed feedback controller 105 compares the speed directive (i.e., target speed) v received from the position feedback controller 101 with an actual traveling speed Vn of the controlled body 107. In order to make the speed v consistent with the speed Vn, the speed feedback controller 105 performs a speed feedback control and generates a manipulated variable u to be given to the controlled body 107.
The speed directive v outputted from the position feedback controller 101 is not directly inputted to the speed feedback controller 105. The speed directive V is inputted as a speed directive vf of which upper limit is limited to a target speed Vt by a speed directive corrector 103. That is, if the speed directive v from the position feedback controller 101 is not more than the target speed Vt, the speed directive v is inputted to the speed feedback controller 105 as is. When the speed directive v from the position feedback controller 101 exceeds the target speed Vt, the target speed Vt is inputted to the speed feedback controller 105.
As noted above, the motor control device 100 of FIG. 25 is designed to perform a cascade control consisting of two types of feedback loops. More particularly, the motor control device 100 is configured to include a cascade control system having position information as the major feedback and speed information as the minor feedback. Accordingly, high precision is achieved in stopping the controlled body 107 at the target stop position Xt.
However, in the motor control device 100 configured with the cascade control system as above, active operation of the position feedback control often inhibits a stable speed change during a deceleration period.
The present invention is made to solve the above problem. It would be desirable that a speed change during a deceleration period may be stabilized in performing a speed feedback control of a motor which drives a body.